Although cardiac surgery is associated with a high rate of allogeneic blood transfusion, evidence about the optimal protocol for blood transfusion for patients undergoing heart surgery is lacking. The rationale for treatment is based on the fact that anaemia is an independent risk factor for morbidity and mortality following cardiac operations, but transfusions themselves have also been associated with high rates of morbidity and mortality in some recent studies.
The Transfusion Requirements After Cardiac Surgery Trial (TRACS) recruited 502 consecutive adult patients who underwent cardiac surgery. Patients were randomly assigned to a liberal strategy of blood transfusion (to maintain a haematocrit ≥30%) or to a restrictive strategy (haematocrit ≥24%). A composite end point of 30-day all-cause mortality and severe morbidity (cardiogenic shock, acute respiratory distress syndrome, or acute renal injury requiring dialysis or haemofiltration) was used. A non-inferiority margin of an 8% clinically important increase in occurrence of the composite end point was used.
A total of 198 of 253 patients in the liberal strategy group (78%) and 118 of 249 (47%) in the restrictive-strategy group received blood transfusion (p<0.01). Nonetheless, occurrence of the primary outcome measure was similar between the two groups (10% liberal vs 11% restrictive; p=0.85). Of note, independent of the transfusion strategy, the number of transfused red blood cell units was an independent risk factor for clinical complications or death at 30 days (HR for each additional unit, 1.2; p=0.002).
This study found no difference in outcomes following cardiac surgery in patients given liberal versus restrictive blood transfusions but the number of units transfused was found to be an independent risk factor for complications or death. In a separate study in the same journal, an enormous variation in transfusion rates following coronary artery bypass grafting was found across US hospitals. Taken together, these studies suggest that blood transfusions following cardiac surgery are currently overused.
▶ Hajajr LA, Vincent JL, Galas FRBG, et al. Transfusion requirements after cardiac surgery: the TRACS randomized controlled trial. JAMA 2010;304:1559–67.
▶ Bennett-Guerrero E, Zhao Y, O’Brien SM, et al. Variation in the use of blood transfusion in coronary artery bypass graft surgery. JAMA 2010;304:1568–75.